diff --git a/Library/Homebrew/extend/ENV/std.rb b/Library/Homebrew/extend/ENV/std.rb
index 5c228d84ad..3c4904f976 100644
--- a/Library/Homebrew/extend/ENV/std.rb
+++ b/Library/Homebrew/extend/ENV/std.rb
@@ -41,7 +41,7 @@ module Stdenv
 
     unless HOMEBREW_PREFIX.to_s == '/usr/local'
       # /usr/local is already an -isystem and -L directory so we skip it
-      self['CPPFLAGS'] = "-isystem #{HOMEBREW_PREFIX}/include"
+      self['CPPFLAGS'] = "-isystem#{HOMEBREW_PREFIX}/include"
       self['LDFLAGS'] = "-L#{HOMEBREW_PREFIX}/lib"
       # CMake ignores the variables above
       self['CMAKE_PREFIX_PATH'] = "#{HOMEBREW_PREFIX}"